New methods in molecular genetics are providing insight into the many possible mechanisms of genetic damage. This understanding is the key to improving our ability to evaluate the biological risks to humans caused by exposure to chemicals in the environment. The long-term objective of this proposal is to establish and conduct high-throughput gene expression assays for monitoring cellular responses to potentially hazardous chemicals. To meet this objective, the use of novel mass-labeled oligonucleotide probes in conjunction with mass spectrometry will be demonstrated for monitoring mRNA expression levels in chemically treated mammalian cells. In addition, procedures for preparation and treatment of various types of cell lines, including cell lysis and preparation of the mRNA in a form ready for hybridization and analysis, will be optimized. This technology has much promise as a approach that will enable toxicologists to investigate chemical effects at the molecular level at a much lower cost than is currently possible.